Interpretive Summary: Oxidative stress in the fat and the liver has been linked to the development of obesity and fatty liver disease. Proteins called NADPH oxidase (NOX) enzymes produce oxidative stress by making oxygen into superoxide radicals. The current study was designed to determine if one of these enzymes, NOX2, plays a role in development of obesity after high fat feeding. Wild type mice and mice lacking an essential NOX2 component were fed low or high fat diets (HFD) for 13 weeks. Female HFD mice with an inactive NOX2 enzyme did not develop obesity. Resistance to getting fat was associated with increased burning of fat in the liver and increased whole body energy use. Fat cell formation and increases in fat cell size were also blocked in female HFD mice lacking active NOX2. HFD mice of both sexes lacking active NOX2 were also protected against development of fatty liver. These data suggest that NOX2 plays an important role in development of obesity.

Technical Abstract:
Oxidative stress in the fat and the liver has been linked to the development of obesity and the metabolic syndrome. However, the molecular origin of reactive oxygen species and the role of these in obesity remain areas of active investigation. The NADPH oxidases (NOX) enzymes are a major source of ROS producing superoxide from molecular oxygen and have been implicated in regulation of cell function. The current study was designed to determine if NOX2 plays a role in development of obesity after high fat feeding. Wild type (WT) mice and mice lacking an essential NOX cofactor p47phox without which NOX2 is inactive (P47KO mice) were fed control diets or high fat diets (HFD) containing 45% fat and 0.5% cholesterol for 13 weeks from weaning. Fat mass and fat cell size were increased to a similar degree by HFD in males. However, female P47KO-HFD mice did not develop obesity. Resistance to HFD-driven obesity was associated with increased burning of fat in the liver and increased whole body energy expenditure. Gene array analysis revealed dramatically lower expression of genes linked to energy metabolism, fat cell formation, and fatty acid uptake in fat pads from female P47KO-HFD mice compared to WT-HFD females. P47KO-HFD mice of both sexes were resistant to the development of insulin resistance and fatty liver and had reduced blood fat and lower leptin and adiponectin hormones relative to WT-HFD mice (P<0.05). These data suggest that NOX2 is an important regulator of energy metabolism and fat cell formation and that NOX2 plays an important role in development of diet-induced obesity.